Patent Documents 1 and 2, for example, introduce a spiral spring assembly used to bias a seat back of a reclining seat. FIG. 34 is a pattern diagram showing a spiral spring assembly.
As shown in FIG. 34, a spiral spring assembly 900 includes a non-contact spiral spring 901, a central shaft 902, and a pin 903. The central shaft 902 connects a seat cushion (not shown) to a seat back (not shown). The seat back is capable of tilting relative to the seat cushion in a front-rear direction about the central shaft 902.
The pin 903 is fixed to the seat back. The non-contact spiral spring 901 is disposed on both axial ends of the central shaft 902. The non-contact spiral spring 901 includes an outer end 901a and an inner end 901b. The outer end 901a is hooked onto the pin 903. The inner end 901b is fixed to the central shaft 902.
When the seat back is tilted rearward, the pin 903 tilts rearward together with the seat back. As a result, the non-contact spiral spring 901 tightens. This tightening causes elastic energy to accumulate in the non-contact spiral spring 901. The elastic energy is used as biasing energy when the seat back is tilted forward.    [Patent Document 1] Japanese Patent Application Publication No. JP-A-H6-296526    [Patent Document 2] Japanese Patent Application Publication No. JP-A-2004-97257